2019 Update - good article about Knotweed in Slate magazine.
 
 
Japanese Knotweed, never the prettiest plant either by reputation or looks, has been more noticeable the past few weeks on the margins of  I-95 and local roads, having just finished flowering. It has been identified as being an invasive pest for over 100 years, I recall it alongside streams as a kid, and thinking it was bamboo. My friends and I would run through  knotweed thickets and use the stems as swords and spears. Today its much more widespread -  and just as pernicious.  Fortunately for small blessing, since there are only female Japanese knotweed plants, the presence of flowers doesn't mean its reproducing since there is no fertilization via pollen. This is certainly not to say that Japanese knotweed cannot colonize new areas, it  spreads quite readily via cuttings and rhizomes.  A piece of root the size of a dime is enough create a new plant, and begin colonizing a susceptible area.
 
In the UK, it  endemic and has been much more visible battle, to the point that any soil with knotweed roots is considered contaminated, and must be disposed of properly.  Yes, it is that pernicious.  There is now a requirement during the mortgage process that the owner has to certify that the property is either knotweed free or it is being actively treated.
 
The best practice for eradication is spray, cut and repeat annually.   The process must be repeated for 5 years to be declared knotweed free.   Why is it  so difficult to get rid of?  One answer - its rhizomes, or roots.  The roots, a large misshapen mass, stretch for  yards in every direction, sits underneath the stems as a source of energy, and has enough strength to push its shoots through any crack.  If the foliage and stems are removed, the plant has enough energy stored in its roots to push up additional stems, again and again.  Once the stems are through the soil, photosyntheisis takes over and the energy that was expended by the roots to push up the stems, can now be replenished easily due to its fast growth.
 
Sources and Further Reading:
http://www.invasivespeciesinfo.gov/plants/knotweed.shtml
http://wiki.bugwood.org/Archive:BCIPEUS/Japanese_Knotweed
 

Wetlands in the News

28 March 2024